Car cutting power and bucking...
 

Ok, I have just had this start occuring. I'm driving around town nice and calm, start slipping the clutch when the light goes green and... the car just cuts power on me while I'm working the clutch. Next, I'm cruising around a parking lot in 1st gear, maybe 2k rpm and it starts violently bucking. I also notice that when I go 75% throttle, get about 5psi boost and then start slowly backing off the throttle, it will sort of buck and hesitate. Then while rev-ing to clear the motor of fuel on a cold shut-down I notice that while I'm holding the car steady at 3k, it's sputtering and popping a LOT more than usual, but it's not backfiring.

I don't believe I have a grounding kit, and I'm looking into one. I've done some searching of the boards and I can't get a definitive answer as to whether my symptoms are all due to grounding.

Basic question, what are the other possible causes of this?

How is its idle?

It idles kinda well. A very little bit of hunting during warm up. For some reason while warming up every time I pull up to a light and pull it out of gear, the revs fall straight to 4-500rpm and bounce back. It only bounces once then catches itself. It has never done that before. Hot idle is steady at 850-900.

I should let you know that I'm highly modded. Single turbo, PFC, large street-port. I just talked to Rotary Performance and they tell me to get a voltage meter and check the voltage on the engine block vs. the chassis. If a drop bigger than .1v is present, I will need grounding. I HOPE TO GOD it is just grounding. I'm not in the position to be doing anything more extensive than that.

any smoke? black?

No, not really. I've had some reports of white smoke from other people but that is either during a humid warm up or right under 7500rpm at WOT. I'm not losing coolant and my coolant temp doesn't skyrocket when I boost.

I know for sure it is just running poorly due to something other than a bad motor or any other mechanical failure. I seems to just be acting like the computer is confused.

I've had similar symptoms with a bad ECU. They are cheap enough used its worth a try swapping out after you check out a few more things.

Have you checked your TPS? What condition are the vacuum lines in? You can also try pulling codes from your ECU at the diagnosis port by jumping the TEN and GND terminals.

I assume by going single turbo that you have upgraded injectors?

If so.. and I know this sounds like a stupid question, have you either used resistors on your Low impedance Injectors, or an injector driver?

That just flew right over my head...

I have 550/1600 and it was all done by Rotary Performance. I trust they did it all right.

At WOT all the way through the revs the car seems fine. Maybe a little of a shudder around 4k.

I have not changed a single thing on the car to cause this. It used to run just perfect.

If a performance shop installed them, then I'm sure they've done it right.

The reason I asked that, is that if you haven't installed resistors or an injector driver, you can eventually blow the injector drivers in the power FC as they are designed for high impedance injectors (standard ones) - and this could cause the problems you are having. I guess we can eliminate that now.

I think grounding does sound probable at this point, assuming the engine is in good shape.

Sounds like a grounding or TPS issue.

Oh yeah forgot to answer that part. TPS has been set to within .03v of spec. VTA1 and VTA2 are reading .44 and 1.03 (I may have those numbers backwards.)

I've been having this similar problem. Glad someone else posted this.

Also, this may be a real noob question, but is it possible to have this problem from not driving the car hard enough? I've only owned my fd for a week now and have never been wot. Should I just go try to clean it out?

Sorry for hijacking your thread.

I dont think a car can act like this due to a carb'd up engine. Maybe it could be as a long term effect but i dont think it can be this severe just out of nowhere. Unless you saw the problem happen gradually.

If you drive your car pretty often with some redlines in there, i dont think that could be a problem.

To the OP, i would check the map?

Yeah I thought the same thing. I haven't been on the car hard lately. But I pulled a trailing plug from under the hood because I could reach it from the top and it looked fine. Then a few days later I said screw it and I threw the car on jack stands, got under there and pulled all the plugs out. To my amazement the trailings were normal but the leadings were basically bridged by carbon. I guess that has something to do with using factory #9's in all 4 and driving it softly. But I replaced them with new ones turned the car on and it idled nice and calm as usual. Went for a drive and... bucking like a mofo. So that wasn't the issue. Now I'm here with new plugs and a poorly operating 7.

Just have RP take a look at the car.

With those prices.... No sir.

BTW we checked the voltage today and it turns out that my grounds are perfectly fine. And today it is driving perfectly fine. I guess maybe RP's tune isn't very friendly to cold weather...

Weird...

My memory is really bad but I think I remember the few times I drove the car last winter, it was acting up. BDC can probably tune it out. GO BDC!:icon_tup: